Lubricating oil and uses thereof

ABSTRACT

Herein disclosed is a lubricant oil or lubricant for the compressor of a refrigeration system which operates with a refrigerant comprising at least one component of the hydrocarbon (HC) group of refrigerants, (a) whereby the lubricant consists of at least 85 weight % of alkylbenzene having an average molecular weight of ≧160 g/mol and exhibiting a viscosity of 2.2-3.0 centistokes (cSt) at 40 deg C.; optionally wherein the alkylbenzene consists of at least 85 wt % of linear (straight chain) alkylbenzene, having an average molecular weight of ≧160 g/mol and exhibiting a viscosity of 2.2-3.0 centistokes (cSt) at 40 deg C.; (b) or alternatively whereby the lubricant consists of at least 85 weight % of alkylbenzene having an average molecular weight of ≧190 g/mol and having a viscosity of 2.5-3.5 cSt at 40 deg C.; optionally wherein the alkylbenzene consists of at least 85 wt % of linear (straight chain) alkylbenzene, having an average molecular weight of ≧190 g/mol and exhibiting a viscosity of 2.5-3.5 centistokes (cSt) at 40 deg C.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent application No. 61/810,800 filed Apr. 11, 2013, the disclosure of which is hereby incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND

1. Field of the Invention

This invention relates generally to lubricating oil composition and uses thereof. In particular, this invention discusses low viscosity lubricating oil, suitable in applications such as in a refrigeration machine that utilizes a hydrocarbon based refrigerant.

2. Background of the Invention

The use of hydrocarbon refrigerants R600a [iso-butane, CH(CH₃)₂CH₃] and R290 (propane, CH₃CH₂CH₃) as replacements for HCFC [hydrochlorofluorocarbon] and HFC [hydrofluorocarbon] compounds is expanding due to both hydrocarbon refrigerants having negligible global warming potential and an ozone depletion potential (ODP) of 0.0.

Recent concerns regarding global warming impact by HCFC and HFC gases such as HCFC R22 [chlorodifluoromethane, CHClF₂], and HFC R134a [1,1,1,2-tetrafluoroethane, CH₂FCF₃] have led to increased use of hydrocarbons as refrigerant for a range of refrigeration systems, most notably in domestic refrigerators and freezers.

The selection of hydrocarbon refrigerants for these applications requires an appropriate selection of compressor lubricant, in order that the refrigeration system functions efficiently and demonstrates compatibility of all components therein.

For refrigeration systems utilizing hydrocarbon refrigerants, U.S. Pat. No 7,758,768 describes the application of alkylbenzene type lubricant. This lubricant oil presents advantages with respect to maintenance of lubricity and refrigerant miscibility at low temperatures described as being generally below 10 deg C., whilst ensuring compatibility with hydrocarbon (HC) refrigerant and the inner compressor environment. It further provides a lubricant composition based on said alkylbenzene and additives selected from those that are known to one skilled in the art as efficacious in refrigeration lubricants.

Although U.S. Pat. No 7,758,768 presents certain advantages, such composition does not take account of the low temperature miscibility from the perspective of evaporator temperatures commonly encountered of <−20 deg C., and the energy efficiency improvements achievable by further reduction of the kinematic viscosity of the compressor lubricant whilst ensuring maintenance of efficient hydrodynamic and boundary lubrication. Similarly, it does not take account of the high temperature lubricant properties with respect to ensuring that they are suitable for the maximum system temperature encountered.

Hence, there is need for further development of lubricating oil compositions.

SUMMARY

Herein disclosed is a lubricant oil or lubricant for the compressor of a refrigeration system which operates with a refrigerant comprising at least one component of the hydrocarbon (HC) group of refrigerants, (a) whereby the lubricant consists of at least 85 weight % of alkylbenzene having an average molecular weight of ≧160 g/mol and exhibiting a viscosity of 2.2-3.0 centistokes (cSt) at 40 deg C.; optionally wherein the alkylbenzene consists of at least 85 wt % of linear (straight chain) alkylbenzene, having an average molecular weight of ≧160 g/mol and exhibiting a viscosity of 2.2-3.0 centistokes (cSt) at 40 deg C.; (b) or alternatively whereby the lubricant consists of at least 85 weight % of alkylbenzene having an average molecular weight of ≧190 g/mol and having a viscosity of 2.5-3.5 cSt at 40 deg C.; optionally wherein the alkylbenzene consists of at least 85 wt % of linear (straight chain) alkylbenzene, having an average molecular weight of ≧190 g/mol and having a viscosity of 2.5-3.5 cSt at 40 deg C.

In an embodiment, a combination of the lubricant oils as described above in (a) and (b) is disclosed. In an embodiment, the total amount of carbon atoms in the alkylbenzene is in the range of 12-18, or alternatively in the range of 13-17, or alternatively in the range of 14-16. In an embodiment, the alkylbenzene alkyl chain consists entirely of a single alkyl chain length. In another embodiment, the alkylbenzene alkyl chain is 100 wt % C8, or C9, or C10, or greater than 50 wt % a single carbon number alkyl chain in the range of C8-C10 and less than 50 wt % other carbon numbers in the same range.

The number of alkyl groups in the above described lubricant oil or lubricant in the alkylbenzene is 1-2.

For the above described lubricant oil or lubricant, the lubricant is a majority distillate component containing at least 95 weight % of linear alkylbenzene having an average molecular weight of ≧160 g/mol and exhibiting a viscosity of 2.2-3.0 centistokes (cSt) at 40 deg C., or alternatively a majority distillate component of at least 95 weight % of linear alkylbenzene having an average molecular weight of ≧190 g/mol and having also a viscosity of 2.5-3.5 cSt at 40 deg C.

For the above described lubricant oil or lubricant, the refrigerant utilized in the refrigerant system comprises at least the refrigerant R600a or R290.

In an embodiment, a lubricant composition is described containing the lubricant oil or lubricant as described above and up to 5 weight % of additives selected from those that provide improved antiwear properties, extreme pressure resistance, oxidation stability, corrosion inhibition, antifoaming, suppressant of pour point, improvement of viscosity index, and reduction of acid content.

For the above described lubricant composition or lubricant (oil), the lubricant demonstrates a kinematic viscosity at 40 deg C. of 2.2-3.5 cSt and exhibits full miscibility with refrigerant R600a over the entire temperature range of +60 deg C. to −60 deg C., and optionally demonstrates a flashpoint of at least 112 deg C.

For the above described lubricant composition or lubricant (oil), the lubricant demonstrates a kinematic viscosity at 40 deg C. of 2.2-3.5 cSt and exhibits full miscibility with refrigerant R290 over the entire temperature range of +60 deg C. to −60 deg C., and additionally demonstrates a flashpoint of at least 112 deg C.

For the above described lubricant composition or lubricant (oil), the lubricant demonstrates a pour point of at least −40 deg C.

For the above described lubricant composition or lubricant (oil), the lubricant demonstrates a dielectric strength of at least 25 kV.

Herein also disclosed is a method of using the above described lubricant composition or lubricant (oil), for example, in a refrigeration system's compressor.

In an embodiment, a compressor is charged with the above described lubricant composition or lubricant (oil).

In an embodiment, a refrigeration system comprises the above described lubricant composition or lubricant (oil), and a refrigerant selected from one component of the hydrocarbon class of refrigerants.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other embodiments for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

DETAILED DESCRIPTION

Overview. In an embodiment, the instant disclosure describes a lubricating oil for a refrigeration compressor, said compressor and associated refrigeration system being of a type which utilizes a refrigerant from the hydrocarbon (HC) group, most particularly refrigerants R600a (iso-butane) and R290 (propane). The lubricating oil consists of an alkylbenzene which contains at least 85 weight % of alkylbenzene having an average molecular weight of ≧160 g/mol and having also a viscosity of 2.2-3.0 centistokes (cSt) at 40 deg C. In another embodiment, the alkylbenzene may also contain at least 85 weight % of alkylbenzene having an average molecular weight of ≧190 g/mol and having also a viscosity of 2.5-3.5 cSt at 40 deg C. In a further embodiment, a lubricant composition consists of the aforementioned alkylbenzenes and one or more additives of a type beneficial to performance aspects of the lubricating oil, for example, additives to enhance resistance to extreme pressure and improve antiwear properties.

In some embodiments, the instant disclosure describes an alkylbenzene lubricating oil to be used in the compressor of refrigeration machines, which operate with a refrigerant consisting of a minimum of one component from the hydrocarbon (HC) refrigerant group, most particularly refrigerant R600a and/or R290.

In some embodiments, the instant disclosure presents said lubricant oil which demonstrates superior miscibility, even under lowest refrigeration system evaporator temperatures, whilst enabling further system energy efficiency improvements via kinematic viscosity reduction of the lubricant, and whilst still maintaining efficient hydrodynamic and boundary lubrication. Some embodiments further enable such low temperature refrigerant miscibility properties and kinematic viscosity reduction to be achieved whilst maintaining appropriate high temperature properties of the lubricant with regard to the maximum system operation temperature.

In an embodiment, a refrigeration system comprises an alkylbenzene lubricating oil and at least one component of the hydrocarbon (HC) class of refrigerants. In an embodiment, a refrigeration system consists of an alkylbenzene lubricant and a hydrocarbon (HC) refrigerant.

In an embodiment, the lubricant comprises an alkylbenzene oil which contains at least 85 weight % of alkylbenzene having an average molecular weight of ≧160 g/mol and having also a viscosity of 2.2-3.0 centistokes (cSt) at 40 deg C. In an alternative embodiment, the alkylbenzene contains at least 85 weight % of alkylbenzene having an average molecular weight of ≧190 g/mol and having also a viscosity of 2.5-3.5 cSt at 40 deg C.

In an embodiment, a lubricating oil composition for use in a refrigeration system consists of at least one component of the hydrocarbon (HC) class of refrigerants, said composition being either of the alkylbenzene lubricants described above or in combination, and an additive selected from those providing an anti-wear or extreme pressure resistance function. In an embodiment, a lubricating oil composition for use in a refrigeration system comprises at least one component of the hydrocarbon (HC) class of refrigerants, said composition being either of the alkylbenzene lubricants described above or in combination, and an additive selected from those providing an anti-wear or extreme pressure resistance function.

In an embodiment, a refrigeration machine is described containing the aforementioned lubricant oil or composition and a refrigerant consisting of at least one component from the hydrocarbon (HC) class of refrigerants.

In some embodiments, the lubricating oil and the lubricant composition of this disclosure are described for application with refrigerants which contain at least one component of the hydrocarbon (HC) group. Examples of such application include use in conjunction with refrigerants R600a (iso-butane) and R290 (propane). Refrigeration machines in which the lubricating oils and lubricant composition are of the type suitable for operation with hydrocarbon refrigerants, and may include (but is not exclusive to) refrigeration systems for domestic use which utilize hermetic compressors.

In an embodiment, a lubricating oil of this disclosure is one of the following:

1. Consisting of at least 85 weight % of alkylbenzene having an average molecular weight of ≧160 g/mol and also exhibiting a viscosity of 2.2-3.0 centistokes (cSt) at 40 deg C. More particularly, the alkylbenzene may also consist of at least 85 wt % of linear (straight chain) alkylbenzene, having an average molecular weight of ≧160 g/mol and also exhibiting a viscosity of 2.2-3.0 centistokes (cSt) at 40 deg C.

2. Consisting of at least 85 weight % of alkylbenzene having an average molecular weight of ≧190 g/mol and having also a viscosity of 2.5-3.5 cSt at 40 deg C. More particularly, the alkylbenzene may also consist of at least 85 wt % of linear (straight chain) alkylbenzene, having an average molecular weight of ≧190 g/mol and having also a viscosity of 2.5-3.5 cSt at 40 deg C.

3. A combination of the two aforementioned alkylbenzene oils, with resultant kinematic viscosity being in the range of 2.2-3.5 cSt.

4. The aforementioned alkylbenzene oils and additive used at a concentration up to 5% by weight selected primarily but not exclusively from those providing a primary function of anti-wear or extreme pressure resistance.

In some embodiments, the lubricating oil composition of this disclosure enables refrigeration system energy efficiency improvements via achievement of a suitably low kinematic viscosity of the lubricant, whilst maintaining efficient hydrodynamic and boundary lubrication, whilst enabling superior low temperature refrigerant miscibility properties for system efficiency, and appropriate high temperature properties with regard to the maximum system operation temperature.

The lubricating oil compositions as described above do not restrict the molecular structure of the alkylbenzene, other than the average molecular weight. In various embodiments, in order to achieve the appropriate technical advantages detailed herein, the alkylbenzene is selected from those alkylbenzene oils containing 75% by weight or more, more preferably 85% by weight or more, and most preferably 95% by weight or more of linear (straight chain) alkylbenzenes with respect to molecular structure. In further embodiments, it is most preferable to select straight chain alkylbenzene oils with the total amount of carbon atoms being in the range 12-18, more preferably in the range 13-17, and most preferably in the range 14-16. In an embodiment, the alkylbenzene may consist entirely of a single total carbon number, for example 100 wt % C14, C15 or C16, or preferably contains a majority of one total carbon number in the range C14-C16 and minority quantities of other carbon numbers in the same range.

In an embodiment, the number of alkyl groups in the alkylbenzene is defined as 1-2, i.e. monoalkylbenzenes or dialkylbenzenes.

In some embodiments, the alkylbenzene oil of this disclosure is produced by blending of separate alkylbenzenes. In some embodiments, the alkylbenzene oil of this disclosure is produced by using a majority distillate component containing at least 95 weight % of linear alkylbenzene having an average molecular weight of ≧160 g/mol and also exhibiting a viscosity of 2.2-3.0 centistokes (cSt) at 40 deg C., or alternatively a majority distillate component of at least 95 weight % of linear alkylbenzene having an average molecular weight of ≧190 g/mol and having also a viscosity of 2.5-3.5 cSt at 40 deg C.

In a further embodiment, the manufacture of the alkylbenzene requires an aromatic compound raw material, such as benzene and may also include suitable derivatives thereof. In an embodiment, alkylating agents include medium range linear olefins, although olefins of higher straight chain or branched chains may also be utilized. Suitable alkylation catalysts include, but are not limited to, aluminum tri-chloride or zinc chloride, or acidic catalysts such as, but not limited to, hydrofluoric acid. Once the alkylation reaction has occurred, a process of separation on the intended alkylbenzene from the catalyst and/or by-products is achieved via distillation or other means of separation.

In an embodiment, the lubricating oil composition of this disclosure is used in refrigeration systems containing hydrocarbon refrigerants, most notably R600a or R290. In some embodiments, the alkylbenzene is used satisfactorily as the sole component of the lubricating oil. In other embodiments, the alkylbenzene oil is benefited further from additisation in the form of antiwear agents and extreme pressure resistant agents. The scope of this aspect of the disclosure is not limited only to agents specifically for antiwear and extreme pressure resistance; many additives are multifunctional and provide more than a single benefit to the lubricant composition, and other additives to improve oxidation stability, corrosion inhibition, antifoaming agents, suppressors of pour point, viscosity index improvers, and acid scavengers are in common use for lubricating oils, well known to those skilled in the art, and may be utilized additionally as additives in the lubricant composition of this disclosure. In various embodiments, the additives that are utilized in this lubricant composition do not exceed a total weight % content of 5% of the composition, and preferably do not exceed a total of 2% by weight.

Suitable antiwear and extreme pressure resistant agents include sulphur and phosphorous containing species, preferably phosphorous containing compounds such as phosphorous containing esters and amines, including but not limited to t-butylated triphenylphosphate, tricresyl phosphate and oleyl phosphite.

EXAMPLES

Examples of the linear alkylbenzene oils of the present disclosure are given as follows:

Sample 001: A linear chain alkylbenzene (LAB) with an average alkyl chain length of 9.51 carbon atoms and an average molecular weight of 211.50 g/mol.

Sample 002: A linear alkylbenzene (LAB) with an average alkyl chain length of 8.46 carbon atoms and an average molecular weight of 196.82 g/mol.

Sample 003: A linear alkylbenzene (LAB) with an average alkyl chain length of 8.04 carbon atoms and an average molecular weight of 190.92 g/mol.

The specific C distribution of the 3 examples is given in Table 1.

TABLE 1 LAB Linear total Alkylbenzene Sample Sample Sample carbon mol. wt 001 002 003 atoms (g/mol) (%) (%) (%) C11 148.24 0.00 0.10 0.00 C12 162.26 0.00 0.12 0.00 C13 176.28 0.00 0.18 0.00 C14 190.30 0.00 52.87 96.04 C15 204.32 50.36 46.20 3.55 C16 218.34 48.34 0.51 0.34 C17 232.36 1.01 0.02 0.02 C18 246.38 0.28 0.00 0.05 C19 260.40 0.01 0.00 0.00 Number Average (Mn) 211.50 196.82 190.92 Mol. Wt (g/mol): Average alkyl (C) chain 9.51 8.46 8.04 length:

Comparative examples are provided as follows:

Sample 004: A linear chain alkylbenzene (LAB) with an average alkyl chain length of 10.91 carbon atoms and an average molecular weight of 231.16 g/mol.

Sample 005: A linear alkylbenzene (LAB) with an average alkyl chain length of 10.92 carbon atoms and an average molecular weight of 231.25 g/mol.

Sample 006: A linear alkylbenzene with an average alkyl chain length of 5.02 carbon atoms and an average molecular weight of 148.51 g/mol.

The specific C distribution of the 3 comparative examples is given in Table 2.

TABLE 2 LAB Linear Comparative total Alkylbenzene Sample Sample Sample carbon mol. wt 004 005 006 atoms (g/mol) (%) (%) (%) C6 78.11 0.00 0.00 1.27 C11 148.24 0.00 0.00 97.23 C12 162.26 0.00 0.00 0.00 C13 176.28 0.00 0.00 0.00 C14 190.30 0.04 0.02 0.00 C15 204.32 8.33 7.72 0.14 C16 218.34 24.99 24.60 0.61 C17 232.36 37.76 38.48 0.57 C18 246.38 24.68 26.16 0.18 C19 260.40 4.06 2.99 0.00 C20 274.42 0.14 0.03 0.00 Number Average (Mn) 231.16 231.25 148.51 Mol. Wt (g/mol): Average alkyl (C) chain 10.91 10.92 5.02 length:

The following technical aspects of Examples 001-006 are determined utilizing the following methodologies:

The low temperature miscibility is determined in accordance with Ashrae (Association of Heating, Refrigeration and Air-Conditioning Engineers) Method 86. Specifically, determinations were made utilizing mixtures of lubricant (Examples 001-006) in refrigerant R600/R290 in a 1:99 weight % ratio and a 15:85 weight % ratio respectively. This ratio range represents that most relevant to the conditions within the refrigeration circuit. Assessment of miscibility is undertaken in the region of −60 deg C. to +60 deg C., with the most relevant temperature region with respect to the invention being the low temperature properties due to evaporator temperatures of −25 deg C. and below which are common in HC based refrigeration systems.

The miscibility property of Examples 001-006 in refrigerants R600a and R290 is presented in Table 3. The viscometric and antiwear/extreme pressure resistance properties of Examples 001-006 are presented in Table 4. The high temperature properties of Examples 001-006 are presented in Table 5. The physical properties of Examples 001-006 are presented in Table 6.

TABLE 3 Wt % ratio Lubricant Lubricant: Temperature Example Refrigerant Refrigerant (° C.) Observation 001 R600a  1:99 +60 to −60 Fully miscible R600a 15:85 +60 to −60 Fully miscible R290  1:99 +60 to −60 Fully miscible R290 15:85 +60 to −60 Fully miscible 002 R600a  1:99 +60 to −60 Fully miscible R600a 15:85 +60 to −60 Fully miscible R290  1:99 +60 to −60 Fully miscible R290 15:85 +60 to −60 Fully miscible 003 R600a  1:99 +60 to −60 Fully miscible R600a 15:85 +60 to −60 Fully miscible R290  1:99 +60 to −60 Fully miscible R290 15:85 +60 to −60 Fully miscible 004 R600a  1:99 +60 to −60 Fully miscible (Comparative) R600a 15:85 +60 to −60 Fully miscible R290  1:99 +60 to −60 Fully miscible R290 15:85 +60 to −60 Fully miscible 005 R600a  1:99 +60 to −60 Fully miscible (Comparative) R600a 15:85 +60 to −60 Fully miscible R290  1:99 +60 to −60 Fully miscible R290 15:85 +60 to −60 Fully miscible 006 R600a  1:99 +60 to −60 Fully miscible (Comparative) R600a 15:85 +60 to −60 Fully miscible R290  1:99 +60 to −60 Fully miscible R290 15:85 +60 to −60 Fully miscible

TABLE 5 Comparative Lubricant Lubricant Lubricant Lubricant Lubricant Lubricant Analytical Example Example Example Example Example Example Property Method 001 002 003 004 005 006 Flashpoint COC (° C.) ASTM D- 132 124 121 152 149 68 92

TABLE 4 Comparative Lubricant Lubricant Lubricant Lubricant Lubricant Lubricant Analytical Example Example Example Example Example Example Property Method 001 002 003 004 005 006 Viscosity at 40° C. (cSt) ASTM D-445 3.21 2.53 3.00 4.42 4.31 1.01 Viscosity at 100° C. (cSt) ASTM D-445 1.23 1.09 0.94 1.48 1.48 0.62 Antiwear Property, 4- ASTM D-4172 0.659 0.697 0.855 0.807 0.798 0.704 Ball, 40 kgf load, 0.654 0.725 0.761 0.726 0.782 0.776 1200 rpm, 75° C., 1 hour. 0.674 0.709 0.829 0.771 0.759 0.674 Average 0.662 0.710 0.815 0.768 0.779 0.718 Falex Extreme Pressure ASTM D-3233 300 300 300 300 300 300 (lb) (A) ASTM D-3233 300 300 300 300 300 300 (B)

Kinematic Viscosity determinations are undertaken in accordance with ASTM D-445. Thermal properties (Flashpoint) are undertaken in accordance with the open cup method ASTM D-97. Antiwear and extreme pressure resistance properties were determined in accordance with ASTM D-2783 and ASTM D3233 (A & B). Other comparative technical properties presented are Pourpoint (ASTM D-97), Density at 20 deg C. (ASTM D-1298), Total Acid Value (ASTM D-664) and Water content (ASTM D-1064). Dielectric strength determinations are performed in accordance with IEC156.

TABLE 6 Comparative Lubricant Lubricant Lubricant Lubricant Lubricant Lubricant Analytical Example Example Example Example Example Example Property Method 001 002 003 004 005 006 Moisture (ppm) ASTM D-1064 47.5 26 54.7 72.4 46.4 48.1 Dielectric Strength IEC 156 34 31 26 32 27 21 (kV) Total Acid Value ASTM D-6645 0.001 0.010 0.007 0.000 0.002 0.000 (mgKOH/g) Density (kg/m3) ASTM SD-1298 0.8597 0.8614 0.8568 0.8575 0.8566 0.8592 Pourpoint (° C.) ASTM D-97 <−60 <−70 <−70 <−70 <−70 <−70

The above data illustrate the following:

Miscibility: Optimized lubricant composition with respect to lubricant miscibility in the hydrocarbon refrigerant may be considered to be achieved by ensuring fullest miscibility of refrigerant with lubricant over the range of lubricant weight % likely to be encountered in the refrigeration system, and over the full temperature range encountered in the refrigeration system. Lowest evaporator temperatures commonly encountered for HC refrigerant types may be <−20 deg C. if not appreciably lower. The data demonstrate that for all examples of the invention and also the comparative examples provided, full miscibility across the temperature range of +60 to −60 deg C. is achieved, confirming suitability of all examples with respect to refrigerant miscibility property.

Kinematic Viscosity/Antiwear & extreme pressure resistance: One means of maximizing the energy efficiency of the refrigeration compressor is to reduce the viscosity of the lubricating oil to the lowest achievable whilst still enabling efficient antiwear properties and extreme pressure resistance of the lubricant are retained. The data shown in table 1 and table 4 demonstrates that Examples 001 and 002 are linear alkylbenzenes having an average molecular weight of ≧190 g/mol and having also a viscosity within the range 2.5-3.5 cSt at 40 deg C. Examples 002 and 003 are shown to be linear alkylbenzenes having an average molecular weight of ≧160 g/mol, also exhibiting a viscosity in the range 2.2-3.0 cSt at 40 deg C. By comparison, Examples 004, 005 meet the molecular weight criteria of both ≧160 g/mol and ≧190 g/mol but are not within the viscosity range of either 2.5-3.5 cSt or 2.2-3.0 cSt at 40 deg C. Comparative example 006 meets neither the molecular weight criteria or the viscosity range criteria. It is advantageous with respect to compressor energy efficiency to achieve a suitably low kinematic viscosity of the lubricant, whilst maintaining efficient hydrodynamic and boundary lubrication, therefore consideration of viscosity must be made in conjunction with the antiwear/extreme pressure resistance data. Although differences in viscosity may be of a low order of magnitude, minor improvements in viscosity reduction may represent significant benefits with respect to compressor efficiency. It is shown that all examples 001-006 are comparable with respect to extreme pressure resistance and examples 001, 002 and 006 are superior with respect to antiwear property. Achievement of minimized viscosity with maintenance of lubricity property is therefore best represented (in preferred order) by the examples 006, 002, 003 and 001 accordingly.

Flashpoint: A minimum flashpoint (by Cleveland Open Cup method) of 112 or most preferably 120 deg C. may be considered a minimum acceptable value to ensure safe operation in consideration of the maximum operating temperature to be encountered in the refrigeration system. The data demonstrates that examples 001-003, and comparative examples 004 and 005 meet this criteria, whereas comparative example 006 demonstrates a flashpoint which clearly indicates unsuitability for the intended application.

Dielectric strength: A minimum Dielectric strength value of 25 kV, or most preferably 30 kV may be considered to provide an acceptable level of electrical insulation by the oil in hermetic type compressors of previously described refrigeration systems, the data demonstrates that examples 001-005 meet this required criteria, whereas example 006 demonstrates an inferior electrical insulation property.

Pourpoint, Density/Total Acid Value/Water content: Data for all samples 001-006 is included for the purpose of demonstration that samples are generally comparable and acceptable with regard to basic specification parameters required of alkylbenzene type refrigeration lubricants. Typical specification values which may be anticipated for the intended application would be Moisture 50 ppm maximum, Total Acid Value 0.03 mgKOH/g maximum, and Pourpoint −40 deg C. maximum. Drying techniques are available to modify moisture content of commercial material therefore moisture content as reported is not significant with regard to assessing suitability for the intended application, rather to demonstrate typical values reported are generally within or close to specification and therefore that the dielectric strength values are accurate for commercial material, as this parameter is influenced by water content.

Consideration of the above technical parameters in totality forms the primary objectives of this disclosure. As can be seen from the data presented above, samples 001-003 demonstrate possessing the improved technical attributes as discussed above collectively, in comparison with samples 004-006 whereby aspects of the technical requirements may be met independently but are not achieved collectively.

While preferred embodiments and examples of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, and so forth). Use of the term “optionally” with respect to any element of a claim is intended to mean that the subject element is required, or alternatively, is not required. Both alternatives are intended to be within the scope of the claim. Use of broader terms such as comprises, includes, having, etc. should be understood to provide support for narrower terms such as consisting of, consisting essentially of, comprised substantially of, and the like.

Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims that follow, that scope including all equivalents of the subject matter of the claims. The claims are incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the preferred embodiments of the present invention. The discussion of a reference in the Description of Related Art is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference, to the extent they provide exemplary, procedural, or other details supplementary to those set forth herein. 

What is claimed is:
 1. A lubricant for the compressor of a refrigeration system which operates with a refrigerant comprising at least one component of the hydrocarbon (HC) group of refrigerants, (a) wherein the lubricant consists of at least 85 weight % of alkylbenzene having an average molecular weight of ≧160 g/mol and exhibiting a viscosity of 2.2-3.0 centistokes (cSt) at 40 deg C.; or alternatively (b) wherein the lubricant consists of at least 85 weight % of alkylbenzene having an average molecular weight of ≧190 g/mol and having a viscosity of 2.5-3.5 cSt at 40 deg C.; or alternatively (c) a combination of lubricant (a) and lubricant (b).
 2. The lubricant of claim 1(a) wherein the alkylbenzene consists of at least 85 wt % of linear (straight chain) alkylbenzene, having an average molecular weight of ≧160 g/mol and exhibiting a viscosity of 2.2-3.0 centistokes (cSt) at 40 deg C.; or alternatively the lubricant of claim 1(b) wherein the alkylbenzene consists of at least 85 wt % of linear (straight chain) alkylbenzene, having an average molecular weight of ≧190 g/mol and having a viscosity of 2.5-3.5 cSt at 40 deg C.
 3. The lubricant of claim 1, wherein the total number of carbon atoms in the alkylbenzene is in the range of 12-18, or alternatively in the range of 13-17, or alternatively in the range of 14-16.
 4. The lubricant of claim 3 wherein the alkylbenzene alkyl chain consists entirely of a single alkyl chain length.
 5. The lubricant of claim 4 wherein the alkylbenzene alkyl chain is 100 wt % C8, or C9, or C10, or greater than 50 wt % a single carbon number alkyl chain in the range of C8-C10 and less than 50 wt % other carbon numbers in the same range.
 6. The lubricant of claim 1 wherein the number of alkyl groups in the alkylbenzene is 1-2.
 7. The lubricant of claim 1 wherein the lubricant is a majority distillate component containing at least 95 weight % of linear alkylbenzene having an average molecular weight of ≧160 g/mol and exhibiting a viscosity of 2.2-3.0 centistokes (cSt) at 40 deg C., or alternatively a majority distillate component of at least 95 weight % of linear alkylbenzene having an average molecular weight of ≧190 g/mol and having also a viscosity of 2.5-3.5 cSt at 40 deg C.
 8. The lubricant of claim 1 wherein the refrigerant utilized in the refrigerant system comprises at least the refrigerant R600a or R290.
 9. A lubricant composition containing the lubricant of claim 1 and up to 5 weight % of additives selected from those that provide improved antiwear properties, extreme pressure resistance, oxidation stability, corrosion inhibition, antifoaming, suppressant of pourpoint, improvement of viscosity index, and reduction of acid content.
 10. The lubricant of claim 1, wherein the lubricant demonstrates a kinematic viscosity at 40 deg C. of 2.2-3.5 cSt and exhibits full miscibility with refrigerant R600a or R290 over the entire temperature range of +60 deg C. to −60 deg C.
 11. The lubricant of claim 10, wherein the lubricant demonstrates a flashpoint of at least 112 deg C.
 12. The lubricant of claim 1, wherein the lubricant demonstrates a pourpoint of at least −40 deg C. or a dielectric strength of at least 25 kV.
 13. A method of using the lubricant of claim
 1. 14. The method of claim 13 utilized in a refrigeration system's compressor.
 15. A method of using the lubricant composition of claim
 9. 16. The method of claim 15 utilized in a refrigeration system's compressor.
 17. A compressor charged with the lubricant of claim
 1. 18. A compressor charged with the lubricant composition of claim
 9. 19. A refrigeration system comprising the lubricant of claim 1 and a refrigerant selected from one component of the hydrocarbon class of refrigerants.
 20. A refrigeration system comprising the lubricant composition of claim 9 and a refrigerant selected from one component of the hydrocarbon class of refrigerants. 